With the increased use of remotely controlled anchor windlasses for deploying and retrieving the anchor automatically, anchors require the following characteristics for successful operation: (1) the anchor must exit and enter the retaining anchor roller or davit smoothly, (2) the anchor must set quickly in all types of bottoms, and (3) the anchor must penetrate deeply into the seabed to develop high holding resistance. While numerous forms of anchors have been developed over the years for use by small vessels, both pleasure craft and work boats, all have their disadvantages and as far as is known, none completely fulfill the criteria set forth above.
U.S. Pat. No. 1,974,933 to Taylor, in 1934, discloses the first plow-type anchor and consists of an articulated shank attached to symmetrical plow shaped flukes. While this anchor holds well when set, it has difficulty setting, particularly in a hard seabed, and the hinge in the articulated shank causes difficulty in stowing and releasing the anchor in an automated system.
U.S. Pat. No. 4,397,256 to Bruce, in 1983, discloses an anchor having symmetrical flukes and a fixed connection between the shank and the flukes. Bruce specifies a shank that is of a rotated L shape that results in an anchor that is difficult to stow, retrieve and release.
U.S. Pat. No. 5,138,967 to McCarron et al. discloses a one-piece plow anchor with the shank rigidly fixed to a symmetrical double bladed ploughshare fluke. The flukes are inwardly dish shaped and may be either curved or consist of two or more flat sections with the trailing end portion of the fluke extending substantially obliquely with respect to the central ridge and so that the fluke presents a substantial surface area facing in the direction of the pull on the anchor. The concave leading edge may be either a smooth curve or comprises at least two straight lined segments. In contrast, in the present invention, the flukes are portions of a cylindrical section with the leading edge having a down and outward pointing fin lateral from the joint between the shank and the flukes.
U.S. Pat. No. 5,188,055 to Kershner discloses one- piece plow-type anchor with flukes that have a relatively broad tail portion lateral to the direction of pull on the anchor.
U.S. Pat. No. 5,855,181 to Oxford discloses a fixed shank plow anchor with flukes consisting of flat sections devoid of any downward pointed projections.
U.S. Pat. No. 6,148,758 to Wilkins discloses a plow-type anchor with flukes consisting of triangular flat sections and a pivoting mechanism in the shank.
All plow-type anchors are of the burying type. That is, the anchor when pulled will continue to bury deeper into the seabed until a solid bottom is reached. In hard bottoms this usually occurs when the flukes are buried. However, in soft bottoms the anchor will continue to move downward until even the shank is below the surface of the seabed. Good holding power in all types of bottoms depends on whether or not the anchor will bury itself deeper and deeper when a forward pull is applied.
When the anchor is lowered to the seabed, the anchor will usually be on one of its sides, resting on the forward end of the shank, the forward tip of the flukes and on the aft edge of one of the flukes. When a forward pull is applied to the anchor the tip of the flukes must penetrate the surface of the seabed to start the burying action. As the anchor is buried, the forward motion will upright the anchor. In a hard seabed, such as packed sand or clay, many plow-type anchors have difficulty penetrating the surface.